circles – Output vector of found circles. Each vector is encoded as a 3-element floating-point vector (x,y,radius) .

circle_storage – Memory storage that will contain the output sequence of found circles.

method – Currently, the only implemented method is CV_HOUGH_GRADIENT.

dp – Inverse ratio of the accumulator resolution to the image resolution. For example, if dp=1 , the accumulator has the same resolution as the input image. If dp=2 , the accumulator has half as big width and height.

minDist – Minimum distance between the centers of
the detected circles. If the parameter is too small, multiple neighbor
circles may be falsely detected in addition to a true one. If it is too
large, some circles may be missed.

param1 – First method-specific parameter. In case of CV_HOUGH_GRADIENT , it is the higher threshold of the two passed to the Canny()edge detector (the lower one is twice smaller).

param2 – Second method-specific parameter. In case of CV_HOUGH_GRADIENT
, it is the accumulator threshold for the circle centers at the
detection stage. The smaller it is, the more false circles may be
detected. Circles, corresponding to the larger accumulator values, will
be returned first.